Although many diabetic patients in renal failure, especially children, have potential donors willing to provide both a kidney and islets, the quantity of islets necessary to achieve insulin independence hampers successful islet Tx by partial pancreatectomy from living donors. Project 2 is designed toward developing a tolerance-inducing strategy for curative treatment of end-stage diabetic nephropathy using living donor composite Islet-Kidney (IK) transplantation (Tx). We have previously demonstrated that the strategy of transplanting pre-vascularized islets as part of IKs in large animal models is successful, using far fewer islets than are required for Tx of free, non-vascularized islets. Both renal and islet function were restored by IK Tx across fully allogeneic barriers in nephrectomized diabetic baboons using a clinically relevant immunosuppression protocol. More recently, our preliminary data have shown the successful induction of tolerance of IKs in rhesus monkeys treated with hematopoietic cell Tx in a mother-to-son combinafion. In order to transifion the IK strategy to clinical applicability, and thus justify the additional donor risk required for IK preparation, the present studies are directed toward achieving consistent tolerance induction to IKs with our historical bone marrow (BM) chimerism regimen, as well as determining the minimal degree of pancreatectomy required for successful IK creafion. These studies will be carried out using cynomologous monkeys and our BM Tx condifioning regimen that has already been introduced into human protocols and continues to be refined for more widespread clinical application (see Project 1 of this U19). We will first determine whether tolerance and long-term islet function can be induced reproducibly across both onehaplotype and fully mismatched barriers, in order to determine whether this strategy will be applicable for both living related and unrelated donor combinafions (Aim 1). We will then assess the optimal timing of IK Tx in relafion to BM Tx for tolerance inducfion, as well as assess the minimal donor pancreatectomy required for IK preparation (Aim 2). Finally, we will examine the effects of recipient age, memory T-cells (Tmem), and innate immune reactivity on the inducfion of tolerance, utilizing appropriate strategies, including thymic rejuvenafion, T-mem deplefion (in conjucfion with Project 1) and inhibifion of inflammafion (Core B), respectively, to overcome these anticipated barriers (Aim 3). We will study the effects of adaptive and innate immune factors on tolerance inducfion in collaborafion with Project 3 for all three aims. Among the advantages of this approach in the treatment of end-stage diabefic nephropathy, in contrast to current clinical management, are that it would obviate the need for chronic immunosuppresion, avoid the morbidity associated with whole organ pancreas Tx, and circumvent the long wait list times currenfiy required for deceased donor Tx by providing euglycemia with limited islet volume safely obtained from living donors.